Field of the Invention
The present invention relates to an electrode material for a lithium-ion secondary battery.
Description of Related Art
Cathode materials made of LiMnPO4 are materials which can be expected to have a higher battery reaction voltage and an energy density that is approximately 20% higher than cathode materials made of LiFePO4. Therefore, cathode materials made of LiMnPO4 are expected to be used in secondary batteries for electric vehicles.
However, lithium-ion secondary batteries including a cathode which includes the cathode material made of LiMnPO4 have the following problems. (1) The low electron conductivity of bulk LiMnPO4, (2) the low Li diffusivity of bulk LiMnPO4, and (3) the anisotropic and large volume change of LiMnPO4 crystals which is caused by battery reactions attributed to the Jahn-Teller effect of manganese ions (Mn2+). Due to these problems, in lithium-ion secondary batteries, the activation energy for intercalating and deintercalating lithium ions into and from cathodes becomes high. As a result, in the lithium-ion secondary batteries, sufficient battery characteristics cannot be obtained, and battery characteristics at a low temperature significantly degrade.
In order to improve the battery characteristics of lithium-ion secondary batteries at a low temperature, active studies are underway regarding LiFexMn1-xPO4 (0<x<1) in which some of Mn in LiMnPO4 is substituted with Fe (for example, refer to Japanese Laid-open Patent Publication No. 2013-101883). In LiFexMn1-xPO4, Fe forms a solid solution, and thus electron conductivity among particles improves more than LiMnPO4. As a result, in lithium-ion secondary batteries including a cathode which includes a cathode material made of LiFexMn1-xPO4, high-speed charge and discharge performance improves.